Parovirus Having a CpG-Enriched Genome Useful for Cancer Therapy

ABSTRACT

A parvovirus characterized by a CpG-enriched genome, wherein the genome contains at least 2 additional CpG inserts that are not present in the wild type genome is described as well as the use of said parvovirus, e.g., a parvovirus based on parvovirus H1, LuIII, Mouse minute virus (MMV), Mouse parvovirus (MPV), Rat minute virus (RMV), Rat parvovirus (RPV), Rat virus (RV), vectors based on the foregoing viral species, and/or cells capable of actively producing the foregoing viral species for the preparation of a pharmaceutical composition, e.g., for the treatment of cancer, preferably pancreas carcinoma, hepatoma or lymphoma.

This application is a continuation of application Ser. No. 12/810,410,filed Jun. 24, 2010, which is a national stage of PCT InternationalApplication No. PCT/EP2008/010972, filed Dec. 19, 2008, which claimspriority under 35 U.S.C. §119 to European patent application 07025215.0,filed Dec. 28, 2007, the entire disclosure of which is herein expresslyincorporated by reference.

The present invention relates to a parvovirus characterized by aCpG-enriched genome, wherein the genome contains at least two additionalCpG motifs that are not present in the wild type genome. The presentinvention also relates to the use of said parvovirus for cancer therapy.

Oncolytic viruses such as rodent parvoviuses represent novel tools forcancer treatment. Besides specifically killing cancer cells (oncolysis),these agents also provide danger signals prompting the immune system toeliminate virus-infected tumours. As a consequence of oncolytic events,the innate and adaptive immune systems gain access to tumour antigens,which results in cross-priming and vaccination effects. Rodentparvoviruses are single-stranded DNA viruses possessing “intrinsic”oncolytic activity, i.e. they preferentially replicate in and killcancer cells of both murine and human origin (1). Yet the anticancerefficacy of the most promising candidates for human clinicalapplications (including H-1PV) needs to be improved.

Therefore, it is the object of the present invention to provide improvedparvoviruses for therapeutic uses.

According to the invention this is achieved by the subject mattersdefined in the claims. The present invention is based on the applicant'sfindings that improved oncolytic viruses can be generated by combiningthe beneficial features of oncolysis and vaccination. An oncolyticparvovirus vector was designed with extra CpG motifs in its genomecausing them to accumulate selectively in tumour cells throughamplification of the viral genome, i.e., CpG-motif-containingderivatives of H-1PV were engineered and compared with the parentalvirus regarding their ability to enhance the efficacy of an autologousantitumour vaccine in an established rat model of hepatoma lungmetastasis (2). Two CpG-enriched H-1PV variants (JabCG1 and JabCG2),preserving both the replication competence and the oncolytic features ofthe parental virus were engineered. The viruses were inoculated ex vivointo the vaccine prior to its subcutaneous injection into tumour-bearinganimals. These are conditions where H-1PV fails to exert any significantdirect oncolytic effect on metastases and essentially acts as anadjuvant by modulating how effectively the vaccine triggers anantitumour immune response (3). In keeping with their increased CpGcontent, the JabCG1 and JabCG2 genomes proved in vitro to be more potenttriggers of TLR-9-mediated signalling than wild-type H-1PV DNA.Antitumour activity was evaluated in a rat model of MH3924A hepatomalung metastases, where parental and modified viruses were inoculated exvivo as adjuvants of a subcutaneously administered autologous vaccine.In this setup, which excludes direct oncolytic effects on metastases,the JabCG2 vector displayed enhanced immunogenicity, inducing markers ofcellular immunity (IFN-γ) and dendritic cell activation (CD80, CD86) inmediastinal (tumour-draining) lymph nodes. This led to a significantlyreduced metastatic rate (50%) as compared to other vaccination schedules(H-1PV-, JabCG1-, JabGC-, or mock-treated cells). The CpG motifs can beadded to the H-1PV genome without impairing the ability of the virus toreplicate and lyse tumour cells. Most interestingly, the addition of theCpG motifs can improve the capacity of parvoviruses, e.g., H-1PV, toturn infected tumor cells into a vaccine causing immune stimulation andsuppression of metastases under conditions where the wild-type virus haslittle effect. This is the first demonstration that virus-inducedoncosuppression can be enhanced by modifying the number of activator CpGmotifs in the viral genome resulting in immunostimulation in vivo.

In summary, the present data provide evidence that increasing the numberof immunostimulatory CpG motifs within oncolytic viruses makes itpossible to improve their overall anticancer effect by inducingantitumour vaccination. The fact that parvoviruses selectively replicatein neoplastic cells should restrict CpG motif amplification to the tumorsite, thereby minimising the risk of side effects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Construction and in vitro Properties of CpG-Modified Viruses

(A) Sequences of CpG-containing fragments (with CpG motifs in bold)cloned at the HpaI site of the pSR19 vector. The H-IPV genomeorganisation is schematically represented with the locations of thecapsid (VP1/2), and nonstructural proteins (NS1/2) genes and theirrespective promoters (P4, P38). The positions of HpaII and AclIrestriction sites are also indicated. Boxed sequences in JabCG1represent the PIF-binding motifs.

(B) Southern blot analysis of viral DNA extracted from NBK cells 48 hafter infection (at a multiplicity of 1 replication unit per cell) withthe different CpG viruses (JabCG1, JabCG2, JabGC) or wild type H-1PVserving as a reference. The positions of viral single-stranded DNA (ss),monomer (mRF) and dimer (dab⁻) replicative forms are indicated.

(C) Cell survival measured using the MIT assay and expressed aspercentage of living cells in virus- vs mock-treated cultures. NBK cells(seeded in a 96-well plate at 2×10³ cells/well) were analysed 72h afterinoculation of H-1PV or CpG-modified viruses at indicated multiplicitiesof infection (MOI). Values shown are means from measurements performedin quadruplicates.

(D) Methylation status of viral DNA extracted from NBK cells 48 h afterinfection (MOI 1) either with JabCG2 or H-1PV. After purification, theviral DNA was subjected (or not) to treatment with the indicatedrestriction enzymes. The presence of the viral replicative forms and theshifts in their size after digestion are marked with arrows. Results arerepresentative of three experiments.

FIG. 2: TLR9-Dependent Activation of Macrophages and HEKTLR9 Cells byWild Type and Modified H-1PV DNAs

(A) NO release from RAW 264.7 macrophages. The cells (1×10⁵ per well ina 96-well plate) were pre-activated overnight with recombinant IFN-γ (10U/ml) prior to stimulation with the indicated oligonucleotides (CpG-28,PTOCG1, PTOCG2 and PTOGC) (5 μg/ml) or viral ssDNAs (JabCG1, JabCG2,JabGC, H-1PV) (5 μg/ml); E. coli DNA at the same concentration served asthe positive control. RAW cells treated with medium (MED) supplemented(or not) with IFN-γ or Lipofectamine were included as negative controls.NO levels were determined at 18 hours using the Greiss reaction. Some ofthe ssDNA samples were preincubated with Lipofectamine™2000 (Lip; 1μg/well) before application onto the cells. The ssDNA taken up by theRAW264.7 cells was detected by PCR 18h post treatment using a set ofprimers common for both H-1PV and CpG-modified genomes.

(B) TLR9-dependent signalling in viral DNA-treated cells. HEK cellsstably expressing mTLR9 and containing a NFxB-driven firefly luciferasereporter gene, were seeded in 96 well plates (2×10³ cells per well) andstimulated with the indicated ssDNAs (JabCG1, JabCG2, JabCG, 10 μg/ml).The treatment with cGpCODN-1826 and sCpGODN-1826 oligonucleotides (5μg/ml) served as a negative and positive control, respectively. At 6 hpost treatment, TLR9-mediated induction of NFxB was assessed bymeasuring luciferase activity in cell lysates. Results shown are averagevalues from 3 independent experiments.

FIG. 3: In vivo Anticancer Potential of CpG-Modified Viruses

(A) Rates of lung metastases in rats injected i.v. with MH3924A tumorcells at day 0, vaccinated s.c. with H-1PV or Jab vector-infected andirradiated autologous cells at day 10, and analyzed at day 30.Significant differences (p<0.05) relative to nontreated animals areindicated with asterisk.

(B) RT-PCR detection of immunological marker expression in mediastinallymph nodes from above groups of animals. Data from individual rats areshown, with the corresponding numbers of metastases (over 2 mm indiameter) given on top of lanes. The samples were matched using β-actinas a reference.

Thus, the present invention provides a parvovirus (and aparvovirus-based vector) characterized by a CpG motif-enriched genome,wherein the genome contains at least one CpG motif that is not presentin the wild type genome.

The term “parvovirus” as used herein comprises wild-type or modifiedreplication-competent derivatives thereof, as well as related viruses orvectors based on such viruses or derivatives. Suitable parvoviruses,derivatives, etc. as well as cells which can be used for producing saidparvoviruses are readily determinable within the skill of the art basedon the disclosure herein, without undue empirical effort.

The term “CpG motif” means an oligonucleotide containing or consistingof the dimer 5′-CG-3′, which is, preferably, DNA.

The term “wherein the genome contains at least . . . additional CpGmotifs that are not present in the wild type genome” relates to a genomeof the parvovirus containing the additional CpG motifs in such a waythat (a) the parvovirus retains its capacity to multiply and spread inneoplastic cells and (b) its competence for oncolysis and/orcytopathogenicity is not impaired.

Based on the instructions given in the Examples below the person skilledin the art can determine (a) suitable sites for insertion of CpG motifsand (b) the optimum number of CpG motifs which result in an enhancedadjuvant and therapeutic effect.

The preferred distance between individual CpG motifs is in the range of1 to 200 nt.

In a preferred embodiment of the present invention, the parvoviruscontains additional CpG motifs that are not present in the wild typegenome in the range of 2 to 30, more preferably 6 to 12. In aparticularly preferred embodiment, the parvovirus contains 6 additionalCpG motifs that are not present in the wild type genome.

In another preferred embodiment of the invention, the additional CpGmotifs are inserted into an intron or an untranslated 3′region of agene. Based on the known nucleotide sequences of the genomes of variousparvoviruses that are useful for the purposes of the present inventionthe person skilled in the art can easily determine suitable sites forinsertion of the CpG motifs. Moreover, insertion of CpG motifs can becarried out by standard procedures, e.g., site-directed mutagenesis etc.

In a more preferred embodiment of the parvovirus of the presentinvention, the CpG motifs are inserted into the untranslated region atthe 3′end of the VP transcription unit. Alternatively, the enrichment ofthe parvovirus genome with CpG motifs can be done by alternative codonusage. For example, the codon AGA (coding for arginine) could bereplaced by the codons CGA, CGT, CGG or CGC and for the amino acidsequence Asp-Val the codons AAC-GTT could be used.

In a further more preferred embodiment of the parvovirus of the presentinvention, the CpG motifs comprise the nucleotide sequence AACGTT orGTCGTT.

In a particularly preferred embodiment, the parvovirus of the inventioncontains three AACGTT motifs and three GTCGTT motifs within theuntranslated region at the 3′end of the VP transcription unit.

In one of the most preferred embodiments, the parvovirus of theinvention is based on H-1PV (i.e. derived from H-1PV) and contains thenucleotide sequence SEQ ID NO: 1 5′-GTT AAC GTT TAC AGC TGA CTA GTC TGCTCAG TCT AAC GTT CTT GTCT AIT GTC GTT TAC TAG TCT CTT AAC GTT TCAT CTACTT GTC GTT AAC-3′ within the untranslated region at the 3′end of the VPtranscription unit.

Particular useful parvoviruses are parvovirus H1 (H-1PV) or a relatedrodent parvovirus such as LuIII, Mouse minute virus (MMV), Mouseparvovirus (MPV), Rat minute virus (RMV), Rat parvovirus (RPV) or Ratvirus (RV).

The present invention also provides a pharmaceutical compositioncontaining a parvovirus of the invention or a cell producing saidparvovirus (parvotherapeutic agent), e.g. human 293(T), NBK or rat RG2.

For administration, the parvotherapeutic agent can be combined withsuitable pharmaceutical carriers. Suitable pharmaceutical carriers of atype well known in the art and readily commercially available, includephosphate buffered saline (PBS) solutions, water, emulsions such asoil/water emulsions, wetting agents of various types, sterile solutions,etc. Such carriers can be formulated with the parvotherapeutic agent(s)by conventional formulating methods for administration to the subject ata suitable dose.

Additional pharmaceutically compatible carriers can include gels,biosorbable matrix materials, implantation elements containing thetherapeutic agent, or any other suitable vehicle, delivery or dispensingmeans or material(s).

Patients treatable by the parvotherapeutic agents of the inventioninclude humans as well as non-human animals. Examples of the latterinclude, without limitation, animals such as cows, sheep, pigs, horses,dogs, and cats.

Administration of the parvotherapeutic pharmaceutical compositions to apatient, e.g. a brain tumor patient, may be effected in any of numeroussuitable ways, e.g., by intravenous, intraperetoneal, subcutaneous,intramuscular, topical, intradermal, intracranial, and intratumoraladministration. The route of administration, of course, depends on thenature of the disease and the specific therapeutic agent(s) contained inthe pharmaceutical composition.

If such parvotherapeutic agent(s) comprise infectious virus particleswith the ability to penetrate through the blood-brain barrier, treatmentcan be performed or at least initiated by intravenous injection of theviral therapeutic agent, e.g., H1-PV.

Since long-term intravenous treatment is susceptible to becominginefficient as a result of the formation of neutralizing antibodies tothe viral therapeutic agent, different modes of administration can beadopted after an initial regimen of intravenous viral administration, orsuch different administration techniques, e.g., intracranial orintratumoral virus administration, can be alternatively used throughoutthe entire course of parvoviral treatment.

As another specific administration technique, the parvotherapeutic agent(virus, vector and/or cell agent) can be administered to the patientfrom a source implanted in the patient. For example, a catheter, e.g.,of silicone or other biocompatible material, can be connected to a smallsubcutaneous reservoir (Rickham reservoir) installed in the patientduring tumor removal or by a separate procedure, to permit theparvotherapeutic composition to be injected locally at various timeswithout further surgical intervention. The parvovirus or derived vectorscan also be injected, e.g., into a tumor, by stereotactic surgicaltechniques or by neuronavigation targeting techniques.

Administration of the parvoviral agents or compositions can also beperformed by continuous infusion of viral particles or fluids containingviral particles through implanted catheters at low flow rates usingsuitable pump systems, e.g., peristaltic infusion pumps or convectionenhanced delivery (CED) pumps.

A yet another method of administration of the parvotherapeuticcomposition is from an implanted device constructed and arranged todispense the parvotherapeutic agent to the desired locus, e.g., tumor.For example, wafers can be employed that have been impregnated with theparvotherapeutic composition, e.g., parvovirus H1, wherein the wafer isattached to the edges of the resection cavity at the conclusion ofsurgical tumor removal. Multiple wafers can be employed in suchtherapeutic intervention.

Cells that actively produce the parvotherapeutic agent, e.g., parvovirusH1, or H1 vectors, can be injected into the desired tissue, e.g., tumor,or into a tumoral cavity after tumor removal.

Combinations of two or more of the above-described administration modescan be employed in any suitable manner, e.g., concurrently,contemporaneously, or sequentially.

The dosage regimen of the parvotherapeutic agent is readily determinablewithin the skill of the art, by the attending physician based on patientdata, observations and other clinical factors, including for example thepatient's size, body surface area, age, sex, the particular virus, cell,etc. to be administered, the time and route of administration, the typeof disease, e.g., tumor type and characteristics, general health of thepatient, and other drugs or therapies to which the patient is beingsubjected.

Accordingly, the present invention also relates to the use of aparvovirus according to the present invention or a cell producing saidparvovirus for the preparation of a pharmaceutical composition for thetreatment of a tumor. A preferred tumor is pancreas carcinoma, hepatomaand lymphoma being expected to be particularly amenable to treatmentwith a parvotherapeutic agent of the present invention.

The below examples explain the invention in more detail.

EXAMPLE 1 Materials and Methods

(A) Reagents

Restriction enzymes were purchased from New England Biolabs, Frankfurt,Germany. PCR primers and phosphorothioated oligonucleotides [CpG-28 (4),PTO-CG1, PTO-CG2, PTO-GC] were synthesised by MWG, Ebersberg, Germany.E. coli DNA, IFN-γ, together with stimulatory (sCpGODN-1826) (5), andcontrol cGpCODN-1826 (with inverted GpC motifs) oligonucleotides wereobtained from InvivoGen, France. Lipofectamine™ 2000 was purchased fromInvitrogen, Karlsruhe, Germany. All other reagents were from Sigma,Deisenhofen, Germany.

(B) Cell Cultures Treatment and Assays

The human embryonic kidney cell line HEK-TLR9 stably expressing themouse TLR-9 receptor was a kind gift from Dr. Stefan Bauer (TechnicalUniversity, München, Germany) (6). HEK-TLR9, 293T and NBK fibroblastcell lines, as well as the macrophage RAW 264.7 cells (ATCC, Manassas,USA) were cultured in DMEM. The ACI rat hepatoma cell line MH2934A (2)was cultivated in RPMI. All media were obtained from Sigma andsupplemented with FCS (10%), penicillin (100 units/ml), and streptomycin(10mg/ml).

The cytopathic effect of the different viral isolates was assessed onNBK cells using MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliumbromide) cytotoxicity assay 72 hours post infection. MH2934A cellcultures were γ-irradiated at 15 Gy prior to injection. Both procedureswere performed as previously described (2). The Greiss colour reactionwas used to determine NO levels in RAW 264.7 macrophage culturesupernatants, as reported (8). Luciferase was assayed as previouslydescribed (6). Lipofectamine™ 2000 transfection was carried outaccording to the manufacturer's instructions.

(C) Viruses and Viral DNA Analysis

The JabCG1, JabCG2, and JabGC vectors were constructed by inserting theHpaI-digested fragments depicted in FIG. 1A into the pSR19 vector- aninfectious H-1PV molecular clone (8). Viral vectors were produced asdescribed (8) by transfecting 293T cells with the respective plasmids,followed by infection of NBK cells and purification so as to containless than 2.5 EU/ml endotoxin. Viruses were titred on NBK cells in aninfectious centre assay. Hirt's extraction method was used to isolateviral DNA from either purified virions or infected NBK cells.Replicative viral DNA forms were digested and revealed by Southernblotting (9). The DpnI enzyme cuts only methylated (′) DNA at the GA′TCsequence, with multiple potential sites along the H-1PV genome. TheHpaII enzyme digests DNA at unmethylated C′CGG motifs, five of which arelocated at the right end of the viral genome (see FIG. 1A). The AclIenzyme cuts DNA only at unmethylated cytosines within the AAC′GTTsequence, which was inserted in three copies giving rise to JabCG2 (FIG.1A). All restriction reactions were performed under the conditionsrecommended by manufacturer.

(D) RT-PCR

Total RNA was extracted from mediastinal lymph nodes of treated animalsand reverse transcribed into cDNA, as previously described (2). Thefollowing primers were used to amplify rat cDNAs: for IFN-γ, [SEQ ID NO:2]5′-ATCTGGAGGAACTGGCAAAAGGACG-3′-forward, [SEQ ID NO: 3]5′-CCTTAGGCTAGATTCTGGTGACAGC-3′-reverse; for CD80, [SEQ ID NO: 4]5′-GGCATTGCTGTCCTGTGATTAC-3′-forward, [SEQ ID NO: 5]5′-ACTCAGTTATGTTGGGGGTAGG-3′-reverse); for CD86, [SEQ ID NO: 6]5′-GCTCGTAGTATTTTGGCAGGACC-3′-forward, [SEQ ID NO: 7]5′-CGGGTATCCTTGCTTAGATGAGC-3′-reverse. The sizes of the correspondingPCR products were 290 by (IFN-γ), 314 by (CD80), and 337 by (CD86)Primer sequences for β-actin and H-1PV PCRs have been previouslypublished (2).

(E) Animals and Tumour Model

MH3924A cells were inoculated through the femoral vein of anaesthetisedACI rats (1×10⁵ cells/animal) to induce metastasis, as already described(2). Vaccination was carried out 10 days after metastasis induction. Forthat purpose, MH3924A cells were infected or not with the respectivepurified viruses. After extensive washing with PBS 24 hours postinfection the cells were irradiated and injected subcutaneously (1×10⁶cells/animal) to the rats. The animals were sacrificed 20 dayspost-vaccination. After opening of the thoracic cavity, the trachea wascanulated with a syringe, and the lungs were insufflated with 5-6 ml of2% Indian ink solution in 0.9% NaCl. The white metastatic nodules (size1-2 mm) were visualized on the black background of the lung tissue,after submerging the lungs in Fekette solution (58% Ethanol, 3%Formadehyde, 0.04% glacial acetic acid). The nodules on the surface ofthe organ were counted using a magnifying lens. Mediastinal lymph-nodeswere extirpated after resection of the lungs. All experiments wereperformed in compliance with European and local guidelines.

(F) Statistics

Means and standard deviations were calculated for cell survival,stimulation, and metastasis incidence. The statistical significance ofdifferences in metastatic incidence among the treatment groups ofanimals was assessed by one-way analysis of variance, followed by aparametric Student's unpaired t-test. The difference between individualvalues was considered significant at P<0.05. Instat 2.00® Macintoshsoftware (GraphPad Software, San Diego, Calif.) was used for theanalysis.

EXAMPLE 2 Construction and in vitro Properties of CpG-Modified Viruses

Since replication competence is essential to enabling oncolytic virusesto spread in the target tumour through secondary rounds of infection, aCpG-enriched parvovirus retaining the capacity to multiply and spread inneoplastic cells was constructed. The H-1PV genome is rather small andencodes proteins with pivotal functions in the viral life cycle.Therefore, a stretch of CpG-containing DNA was inserted into anuntranslated region at the 3′ end of the VP transcription unit. Asindicated in FIG. 1A, the sequences cloned into two H-IPV variants(JabCG1, JabCG2) contained different numbers of two types of CpG motif:AACGTT (a general immunostimulatory element, reported to be active inmurine models) (4) and GTCGTT (a motif shown also to activate humancells) (10). A third construct Gab GC) had an inverted (GC) orientationwithin the motifs and served as control.

The genomes of the viruses produced after transfecting 293T cells withthe constructs were sequenced. Upon passaging in both permissive celllines and animals, the JabCG1 virus was found progressively toaccumulate mutations in the inserted CpG motifs (data not shown). It washypothesised that this drift might be due to the presence in JabCG1 ofneighbouring ACGT motifs (FIG. 1A, boxed sequences) constituting bindingsites for the Parvovirus Initiation Factor (PIF) (11). This might reducethe concentration of PIF available for binding to the left-end origin ofthe genome, where its essential function is performed, thus selectingfor mutants which don't bind PIF in the insert. In keeping with thisview, the JabCG2 and JabGC variants (lacking homology with PIF-bindingsites) remained stable through multiple passages (data not shown).

When used in equivalent amounts (genome titres), the JabCG1/2 and JabGCmutants showed the same ability as the parental virus to replicate inand kill transformed NBK cells (FIG. 1 B, C). Thus, none of theinsertions appeared to impair the competence of the virus for oncolysisand propagation. The methylation status of the viral DNA in infectedcells was determined by restriction digestion with methylation-sensitiveenzymes (RFLP analysis). Monomeric and dimeric viral replicative forms(FIG. 1D) were refractory to DpnI digestion. On the other hand, viralDNA was sensitive to HpaII and, in the case of the JabCG virus, to AclI,which recognises some specific sites confined to the CpG insert(AACGTT). Altogether, these results show that the viral DNA replicationproducts, and in particular the cytosine residues present within theincorporated CpG motifs, were largely unmethylated—a prerequisite totriggering TLR-9 activation (5). In conclusion, the CpG motifs added tothe H-1PV genome appeared not to impair viral replication orcytopathogenicity, and remained in the unmethylated form suitable forinteraction with TLR9 receptors.

EXAMPLE 3 TLR9-Dependent Activation of Macrophages and HEKTLR9 Cells byWild Type and Modified H-1PV DNAs

Next the capacity of single-stranded DNA isolated from the differentviruses to stimulate the release of nitrogen oxide from RAW 264.7macrophages preactivated with IFN-γ was tested (7). The cells provedpositive for TLR9 mRNA by RT-PCR (data not shown) and functionallyresponded to E. coli DNA (FIG. 2 A). NO release from RAW 264.7 cellsincubated either with phosphorothioated oligonucleotides (PTO-CG1,PTO-CG2 and PTO-GC), with fragments identical to those used for cloning(see FIG. 1A), or with ssDNA isolated from the respective viruses(JabCG1, -CG2, -GC, or H-1PV) was measured. CpG-28 (a previouslypublished activator oligonucleotide) (4) and E. coli DNA were used aspositive controls. As shown in FIG. 2A, the added CpG motifs of theparvoviral DNA also displayed an activating capacity. The ssDNA ofJabCG2 was more stimulatory than that of JabCG1, despite containingfewer CpG motifs (6 vs 13). This is consistent with the fact that thesemotifs got mutated during propagation of JabCG1. In keeping with earlierreports showing that transfection with a liposome-forming agent canenhance the stimulatory effect of microbial DNA through improvedendosomal delivery (12), higher cellular uptake (as assessed by PCR) wasachieved when Lipofectamine was used to transfect cells with the ssDNAof H-IPV or its CpG-enriched derivatives (FIG. 2B, lower panel). Therelease of NO from RAW 264.7 was correspondingly improved. To confirmthat the ability of JabCG DNA to activate RAW 264.7 cells was due torecognition of the incorporated CpG motifs by TLR9, the stimulatoryeffects of the above-mentioned ssDNAs on HEK293 cells stably transfectedwith mouse TLR9 cDNA was measured. HEK293 cells do not normally expressany TLRs, so TRL9 activation could be monitored through induction of thestably-integrated NF-kB-driven reporter gene (Luciferase). As shown inFIG. 2B, the JabCG1- and JabCG2-derived ssDNAs induced luciferaseexpression to a significantly higher level than JabGC-derived ssDNA, thenegative control oligonucleotide (cGpC-1826), or medium. JabCG DNA,however, had a much lesser activating effect than the positive controloligonucleotide (sCpG-1826), most probably because it contains fewer CpGmotifs per microgram DNA. From these data it can be concluded that H-1PVssDNA has the capacity to trigger immune cell activation and thatCpG-enrichment can enhance this effect via TLR9 activation.

EXAMPLE 4 Arming Parvoviruses with CpG Motifs Improves TheirOncosuppressive Capacity

Due to these results the impact of the inserted CpG motifs on theimmunomodulatory and oncosuppressive activities of H-1PV in vivo wasinvestigated. For this, an established rat lung hepatoma metastasismodel, where the immunostimulatory capacity of parvoviruses can beassessed in the absence of any direct oncolytic effect on target tumourswas chosen. The H-1PV-derived Jab mutants were tested for their adjuvanteffects when administered with a vaccine consisting of X-ray-irradiatedautologous (MH3924A) tumour cells providing only limited protectionagainst metastases in the absence of infection. The virus was inoculatedex vivo into the vaccine prior to its irradiation and subcutaneousinjection into metastasis-bearing rats. In this setup the viruses couldclearly act only as vaccine adjuvants, since they were undetectable byRT-PCR in the lungs of treated rats and thus could not exert any directoncolytic effect on lung metastases. As shown in FIG. 3A, thetherapeutic effect of the cellular vaccine was improved only to aslight, barely significant extent when the adjuvant virus was H-1PV,JabGC, or JabCG1. This is in agreement with the lack or gradual loss ofCpG motifs in these viruses. In contrast, the JabCG2-infected vaccinereduced the metastatic rate by over 50% as compared to non-treatedcontrols. Besides showing a strikingly lower number of nodules above 2mm in size, the group treated with the JabCG2 vaccine displayed no largenecrotic nodules (exceeding 5 mm). In the other treatment groups, incontrast, this advanced stage of the disease was common. The expressionof markers revealing activation of cellular immune response (IFN-γ) andmaturation of dendritic cells (CD80, CD86) was measured by RT-PCR inmediastinal lymph nodes draining the lungs in which metastases werelocated. As illustrated in FIG. 3B, these innate and adaptive immuneresponse indicators were strongly induced in the JabCG2-treated group,correlating with a favourable disease outcome. Most interestingly, thefew animals that showed such marker elevation in the JabCG1 treatmentgroup also had fewer metastases. Altogether these data strongly suggestthat it is possible to reinforce the antitumour capacity of parvovirusesby arming them with CpG motifs that elicit enhanced immune activation.This is best exemplified by the JabCG2 virus, whose improved adjuvantand therapeutic effects clearly correlate with the preservation ofinserted CpG motifs through multiple passages.

Parvoviral oncolysates of human melanomas have recently been shown to bestronger activators of dendritic cell maturation than freeze/thawextracts (13). This effect was found to correlate with induction ofHSP72 expression in the infected tumor cells. The present results showthat this parvoviral immunostimulatory activity can be boosted by addingextra CpG motifs to the viral genome. This means that besides putativevirus-induced cell factors, viral constituents contribute toimmunomodulation. These constituents most likely include viral DNAspecies produced by infected tumor cells.

The small size of the H-1PV genome limits the number of CpG motifs thatcan be introduced into it without interfering with its packaging. Itshould be possible, nevertheless, to double the number of addedactivator CpG motifs, and perhaps to improve further the oncosuppressivecapacity of H-1PV. This may be accomplished either by generating suchmotifs through alternative codon usage or by a viral intron located atthe p38 promoter.

LIST OF REFERENCES

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1. A parvovirus comprising a CpG motif-enriched genome, wherein thegenome contains at least 2 additional CpG motifs that are not present inthe wild type genome.
 2. The parvovirus of claim 1, which contains atleast 5 additional CpG motifs that are not present in the wild typegenome.
 3. The parvovirus of claim 1, which contains between 5 and 20additional CpG motifs that are not present in the wild type genome. 4.The parvovirus of claim 1, wherein said additional CpG motifs aregenerated by alternative codon usage.
 5. The parvovirus of claim 1,wherein said additional CpG motifs are inserted into an intron or auntranslated 3′region of a gene.
 6. The parvovirus of claim 5, whereinsaid untranslated 3′region is the untranslated region at the 3′end ofthe VP transcription unit.
 7. The parvovirus of claim 1, wherein saidCpG motif comprises the nucleotide sequence AACGTT or GTCGTT.
 8. Theparvovirus of claim 1, wherein said parvovirus is parvovirus H1 (H-1PV)or a related rodent parvovirus.
 9. The parvovirus of claim 8, whereinsaid related rodent parvovirus is LuIII, Mouse minute virus (MMV), Mouseparvovirus (MPV), Rat minute virus (RMV), Rat parvovirus (RPV) or Ratvirus (RV).
 10. The parvovirus of claim 1, wherein said parvoviruscontains three AACGTT motifs and three GTCGTT motifs within theuntranslated region at the 3′end of the VP transcription unit.
 11. Apharmaceutical composition containing a parvovirus according to claim 1or a cell producing said parvovirus.
 12. A method for the treatment ofcancer comprising administering a parovirus according to claim 1 or acell producing said parovirus to a patient in need thereof.
 13. Themethod of claim 12, wherein said cancer is pancreas carcinoma, hepatomaor lymphoma.
 14. The parovirus of claim 1 which is replicationcompetent.